This invention relates generally to air conditioning system for automobiles, and more particularly to an automatic control system for such an air conditioner based on dynamic models of the system.
Various types of air conditioning systems have been used and applied for automobiles so as to control the temperature, humidity, cleanliness and so on of the air within a vehicle compartment. Among such various types, an air conditioning apparatus which controls only the temperature has been widely used. In such air conditioning apparatus for automobiles, in order to control the air temperature at air outlets throughout a wide range from a low temperature to a high temperature, air sent in the apparatus is once cooled by a cooler, such as an evaporator, and then the cooled air is heated by a heater, such as a heater core, so as to obtain a desired temperature of the blowing air. This series of apparatus for blowing, cooling and heating air is referred to as blowing air control measure, and the entire system is referred to as an air conditioning unit. Two types of such air conditioning units have been widely used in these days as an air conditioner of automobiles. One of such units is a reheat type which is arranged to change the heat value supplied to a heater. The other is an air-mixing type which is arranged to change the ratio of air passing through the heater.
In either of these two types, the temperature of air within a vehicle compartment is controlled by the heat value of the blow off air, i.e. the flow rate and temperature of the blow off air. The flow rate of the blow off air is determined by the blowing capability of a blower motor or the like. The temperature of the air is determined by the cooling capability of the cooler (evaporator), i.e. the capability of the cooling system including a compressor and heating capability of a heater. This includes, for example, the amount of circulated hot water in the case of a reheat type and the damper opening degree of the air-mixing damper in the case of an air-mixing type.
When an air conditioning unit starts operating, the temperature of air within a vehicle compartment is detected to feedback control the temperature and flow rate of blow off air on the basis of the difference between the detected temperature and a predetermined target temperature. As a result, the temperature of air within the vehicle compartment, which will be referred to as the internal air temperature hereinafter, approaches the setting target temperature gradually, because of the heat value of the blow off air.
Such control of air temperature is disclosed in Japanese Patent Provisional Publications Nos. 55-47914 and 55-77659.
The above-described conventional apparatus is based on feedback control which is performed on the basis of the difference between a detected internal air temperature and a setting target temperature, so that the former approaches the latter. Some conventional apparatus further adopts prediction control in which the amount of control is determined so that predetermined conditions of thermal equilibrium are satisfied considering the external air temperature and solar radiation amount. Furthermore, the amount of air to be blown off is controlled such that the blow off air amount is increased when the difference between the above-mentioned temperatures is large and the blow off air amount is decreased as the difference becomes smaller.
Therefore, transient response at the time of the change of the setting value of the target temperature is not necessarily satisfactory. Thus the transient response is poor depending on the internal air temperature at such instant, the capability of the air conditioning unit or the like. Therefore, there has been a problem, that it is difficult to provide a comfortable environment to vehicle occupants.
While the capability of an air conditioning unit is determined by the combination of the blow off air amount, cooling capability of the cooler, heating capability of the heater and so on, it is difficult to determine what combination of these factors provides an optimal control. Therefore, these factors have hitherto been combined simply by the experience of designers as the above-mentioned control of blow off air amount. Accordingly, the capability of such an air conditioning unit has not hitherto been derived sufficiently.
Additional problems would also arise when the air conditioning unit is controlled in the same manner as in the normal operation at the time of initial turn on of the air conditioner. These problems occuring in this initial state when the control of the air conditioning unit is started are, for example, a reverse control that the internal air temperature is once separated from the target temparture and an excessive control when the internal air temperature rapidly approaches the target temperature.
Furthermore, when the target temperature is set near the limits of the possible control range of the internal air temperature of a vehicle by an air conditioning unit, there is a problem in which the follow-up of the control is deteriorated due to overshoot and so on from the setting target value of the internal air temperature when the control is performed taking into account the deviation between the target temperature and the internal air temperature from the past.